Solar heat transfer system (HTPL), high temperature pressurized loop

ABSTRACT

Delivering heat from modem high temperature solar collectors to storage tanks is more effectively done using a pressurized, high temperature fluid loop using nonflammable and low toxicity heat transfer fluids and is the subject of this patent. Nontoxic water/antifreeze mixtures can be used in pressurized (14#, (14 Pounds Square Inch pressure above atmosphere)) systems up to 265 degrees Fahrenheit before the mixture boils. Boiling under pressure transports either steam or heat out of the closed system. The steam must be condensed and returned to the closed loop system to keep it full. In order to accomplish this in a practical manner a pressurizing cap and overflow reservoir are used. The system will either shed excess heat collected by boiling or limit the heat input from the collector panel by increasing its heat loss due to increasing solar collector temperature above ambient.

BACKGROUND OF INVENTION

[0001] This invention pertains to collection and delivery of heat from aroof or ground mounted solar collector panel to a hot water storage tankvia the use of a pressurized fluid loop. The pressurized loop systemutilizes a water antifreeze mixture or other suitable fluid iscirculated via a pump. In addition the system is protected fromover-temperature and over-pressure if the circulating pump fails. Thehigh temperature fluid heat transfer loop allows for a smaller heattransfer area and hence more compact, hot water tank heat exchanger anda small diameter, approximately 2 Inch diameter, flexible insulatedumbilical containing both electrical and fluid tubing connections,approximately ¼ Inch outside diameter tubing, to go to and from the hotwater tank to the solar collector for ease of installation. The savingin materials for heat exchangers, piping, insulation, and theself-protection from overheating, make this collector system unique.

PRIOR ART

[0002] Most common solar collector systems are un-pressurized and use aheat exchanger external to the water tank to exchange heat from theun-pressurized solar loop to the city water pressure in the hot watertank. Un-pressurized collector heat transfer loops are limited to theboiling point water antifreeze mixtures, typically 50/50, at atmosphericpressure of approximately 220 degrees Fahrenheit. A water antifreezemixture of approximately 50/50, pressurized to fourteen PSI, orapproximately two atmospheres in the collector loop will not boil until265 degrees Fahrenheit. The higher operating temperature in thecollector loop allows for efficient in tank heat exchangers to beutilized, which do not disturb the normal tank stratification. Internaltank heat exchanger also eliminates the pump would circulate water fromthe hot water tank through the external heat exchanger. Thestratification of the normal hot water tank, hot on top and cooler onthe bottom, is disturbed by circulating water from the hot water storagetank, through the external heat exchanger. It is important not todisturb the normal tank stratification, because it decreases the normalgas or electric heater efficiency.

[0003] Some solar collectors use City line water pressure and flow thiscity water through the collector to heat it. These systems are calledintegrated collector storage, roof mounted systems. The city potablewater is subject to freezing and must be heated electrically at night tokeep the collector from freezing during cold weather. Other systems,which circulate potable through the collectors when they're illuminatedby the sun, must drain this water out at night during freezing weather.

[0004] Main advantages: 1) Pressurized heat transfer loop Allows solarcollectors to operate up to 265 degrees Fahrenheit; 2) Pressurized heattransfer loop allows heat to be transferred with very low fluid flowrates minimizing pumping power and allowing small diameter tubes to takefluid to and from the solar collector and water tank heat exchanger; 3)Internal heat exchanger adapts to existing tanks with minimumre-plumbing and without tank removal or draining; 2) Heat exchanger isefficient; 3) Double wall heat exchanger safely separates toxic heattransfer fluids from potable water; 4) This solar system costs less toinstall and maintain; and 5) Solar system maintains normal tankstratification.

SUMMARY OF INVENTION

[0005] In summary, the present invention is a Pressurized fluid loop,where heat is collected in a solar panel illuminated by the sun, heats asolution of water based antifreeze or other suitable liquid, the fluidis pumped at low flow rate to a hot water tank where it gives up theheat via an internal heat exchanger. The fluid loop is pressurized andoperates above the normal boiling point of water 212 Fahrenheit. Thefluid loop also has built in over-temperature and over-pressureprotection built in, so if the fluid circulation pump stops, that thesystem will not get too hot and damage itself.

[0006] The primary objective of the present invention is to reduce theamount of material needed to collect and transport solar heat. This isaccomplished buy increasing the temperature in the fluid loop, whichdecreases the area of the hot water tank to fluid loop heat exchangersurface. The higher fluid temperature difference, between the hot watertank and the solar collector allow more heat to be stored in each unitvolume of fluid in the solar collector heat transfer loop. Hence asmaller volume of fluid, lower flow rate, is needed to deliver the heatfrom the solar collector to the hot water tank. The higher fluidtemperature in the collector will lower the collector's efficiency,since it is loosing heat to the outside air. This loss is a small priceto pay for a system using significantly less material.

[0007] Another objective is to reduce the time and complexity ofretrofitting solar energy to existing homes, since it uses flexiblesmall diameter tubing to carry the low fluid flow volume. The smalldiameter of the fluid carrying tubes, approximately ¼ Inc outsidediameter, also allows them to be thermally insulated and still be lessthan 2 inches in diameter. By adding an electrical wire bundle to theinsulated fluid carrying tubes and wrapping them with a protectivecovering an umbilical cord is created, which carries all fluids andelectrical signals from the hot water tank to the solar collector. Thisplug and play umbilical allows for do-it-yourselfers or professionals toinstall the system more quickly. These fluid carrying tubes can beinstalled in existing buildings, because they are flexible and can befed into and through attics, walls and placed on the outside ofbuildings, without being unsightly.

[0008] Additional objectives, advantages and novel features of theinvention will be set forth in part in the description which follows andin part will become apparent to those skilled in the art uponexamination of the following. Others may be learned by practice of theinvention. The objectives and advantages of the invention may berealized and attained by means of the instrumentalities and combinationsparticularly pointed out in the appended claims.

DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a perspective view of the pressurized loop solarcollector system, including the fluid loop, the solar collector, the hotwater tank heat exchanger, the fluid pump and controller and theover-pressure and pressure activated over-temperature systems.

[0010]FIG. 2 is a view of the over-pressure system and its associatedfluid recovery system, with the external fluid recovery system.

[0011]FIG. 3 is a pressure activated solar collector over-temperaturecontrol system, which opens dampers in the collector to let heat out,when the fluid in the loop boils and raises the loop pressure.

[0012]FIG. 4 is a boiling activated solar collector over-temperaturecontrol system, which forces fluid from the main fluid loop into aliquid to air heat exchanger radiator, to let heat out of the fluidloop, when the fluid in the loop boils

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013] The invention consists of a pressurized heat transfer loop, whichoperates well above the boiling point of water at one atmosphere, 212degrees Fahrenheit (FIG. 1). The water is heated, by the sun, in thesingle, or double glazed, solar collector (1), an integral part of thecollector is a set of damper, which are opened by pressure (15). Thesedampers are only open when the solar heat collected is more than the hotwater tank can use. These dampers when opened allow outside air of lessthan 120 degrees Fahrenheit to flow over the absorber plate, where thesunlight is converted to heat and transferred into the heat transferfluid. This airflow cools the absorber and stops the boiling. Then thedampers close and the absorber heats back up. The dampers open and closeon a 2 to 5 minute cycle and only minor boiling is allowed to takeplace. This self-controlling feature is unique and allows the collectorto protect it self, even if the fluid flow in the pressurized loop (17)stops. Alternatively to the dampers, or along with them one could usethe system shown in (FIG. 4, (29)), which is a pressurized side channelto the main pressurized heat transfer loop, which is at the uppermostpoint in the main fluid loop. As gas bubbles form in the solar collectorthey try to escape by going into the side channel heat exchanger. Thefluid there is below the boiling point of the pressurized fluid and theycollapse and condense. The fluid is the side channel is cooler, becausethe outer surface is exposed to the outside air. If no bubbles areforming in the solar collector, then there is no flow of fluid in theside channel and the fluid the side channel stays cool.

[0014] The system has two possible configurations for activating theheat transfer fluid pump (12). The first is a conventional controlsystem run from household 115 VAC power. This control system has acontrol box (11), which plugs into the wall outlet and has threesensors. The collector has a temperature sensor using low voltage (8)who's electrical wires are part of the umbilical, to tell thecontroller, which turns on the pump, when the collector temperatureexceeds the hot water tank temperature, measured by sensor (10) at thebottom of the hot water tank. There is also a sensor in the top of thetank (9), which tells the controller the tank is getting to hot, ie noone home to use hot water, then the controller will shut off the pump.This would now cause the pressure damper or side channel heat exchangerto protect the collector from excessive boiling, which will block thecollector tubes with scale in time.

[0015] The second pumping system is based on using a photovoltaic array(6), which provides 12 Volt power when the sun is shining. This power iscarried down to the pump on the umbilical connector wire. The pump is aDC powered pump, which is capable of low flow at modest pressures. Thereis no control box. When the sun is out the pump pumps, when it is not,the pump stops. A thermal disconnect switch (18), is place on the top ofthe hot water tank, so if it gets too hot, it will disconnect the pump.

[0016] The internal tank heat exchanger adapter (13), screws into theinlet or outlet port of the hot water tank (14) the house water to beheated now exits or enters the tank now via a side arm of the adapter.The pressurized loop heat exchanger fluid enters and exits the adapterin small diameter copper tubing, like quarter inch outside diametercopper tubing.

[0017] To transport the pressurized fluid and the heat it contains fromthe solar collector to the hot water heater and flexible insulatedumbilical is used (7). The umbilical consists of the thermally insulatefluid connections and the low voltage electrical connections in one easyto run length. The two small diameter copper tubes, hot collector fluidto the hot water tank and cooler fluid retuning from the hot water tankto the collector, are held apart by a spacer, such as a polymer coatingapplied to each, so the can be placed next to each other withouttouching and tied together along their length. This allows the two-tubebundle to be flexible and insulated with a ¾ inch thick insulatingjacket and still be less than 2 inches in diameter. Adding a wire cableto the outside of the umbilical allows sensor (8) to be easily connectedto the controller. The small diameter copper tubes are connectedtogether with standard {fraction (1/4, 5/16)}, or ⅜ unions andT-connectors (5).

[0018] The invention also consists of a pressure relief and fluidoverflow recovery system (FIG. 2). and includes a pressurized fluidreservoir (3), a pressure cap to regulate the pressure in the system,and allow the overflow to return on system cool down at night (2), whichis connected to a fluid overflow and recovery reservoir (4). Thepressure of the fluid in the solar collector heat transfer loop isregulated by the pressure cap, which uses a spring to push against thefluid pressure over a fixed area. During normal daily operation when thesun is out, the heat transfer fluid expands as it heats from 75 degreesFahrenheit to over 230 degrees Fahrenheit and when the pressure reachesthe set pressure, i.e. 16 PSI, fluid overflows to the fluid overflowreservoir (21), which is vented to the atmosphere by a cap (30). Atnight, when the fluid in the solar heat transfer system cools andcontracts, fluid is drawn back into the heat transfer system to keep iffull of fluid and keep air out. Air in the system increases thecorrosion of the fluid loop. This simple system allows the approximately50% water/50% antifreeze mixture in the solar heat transfer loop to heatup to over 212 degrees Fahrenheit, without boiling until it reachesalmost 265 degrees Fahrenheit, at 16 PSI confinement pressure. This hightemperature allows for heat to be transferred more efficiently into thehot water tank, using lower flow rates and an internal (or external) hotwater tank heat exchanger.

[0019] The invention also consists of a pressure activated solarcollector over-temperature protection system (FIG. 3). This systemconsists of a solar system fluid pressure-activated actuator (16), suchas a piston (22), or other pressure-activated actuator, which is in aretracted state at atmospheric pressure and an extended state at thepressure cap relief setting, such as 16 PSI. A spring (20) orpressurized cavity can be used to return the actuator to the retractedstate, when the solar system pressure falls to atmospheric. The solarsystem fluid (21) is sealed into the system via a bellows (23) or otheracceptable seal, such as an O-ring. The actuator is connected to thefluid loop (17).

[0020] This actuator output (24) is connected to a hinged or slidingvalve (25,26), like a furnace damper, which allows air to flow over thesolar collector absorber plate and cool it off with outside air.Over-temperature protection is achieved by successive airflow eventsover the solar collector absorber plate. When the solar collector getstoo hot the heat transfer fluid (21) boils in the collector. This causesthe pressure actuator to extend and open to collector air damper valves,which take the heat out of the solar collector and the heat transferfluid drops below the boiling point and stops boiling. The systempressure returns to atmospheric and the actuator retracts and closes thecollector air damper valves. This cycle repeats itself until the sungoes down, or the fluid flow is reestablished. Thus the collectorprevents damage to the system, by keeping the collector near the boilingpoint of the water/antifreeze mixture, if the hot water tank is hotenough, the pump fails to circulate the heat transfer fluid, or thefluid flow path is blocked. The inset in FIG. 3 shows that the actuatorand air valve position as a function of system pressure. The air valvesare shut and the actuator retracted until a pressure of approximately80% of the system pressure, maintained by the pressure cap is reached.Their air valves are open and the actuator extended by the time thesystem reaches 95% of the system pressure maintained by “the radiatorcap”. This arrangement allows the system to cool itself before vigorousboiling occurs. The pressure vs. actuator position profile is determinedby the piston area (22) and spring (20) constant.

[0021] The invention also consists of a boiling activated solarcollector over-temperature protection system (FIG. 4). The systemconsists of a liquid to air heat exchanger and a boiling gas separator.During normal operation they entire system is full of heat transferfluid (21) and no boiling occurs. The liquid to air heat exchanger (29)is a side arm and normally has no fluid flow in it. Normally the fluidflows into the boiling gas separator from the solar collector and out ofit down to the hot water tank. Under abnormal conditions such ascirculating pump failure or the solar input being greater than the hotwater tank can use, the solar collector will begin to boil. In thisevent the boiling gas separator (28) allows the gas bubbles to go intothe liquid to air heat exchanger (29), which stirs the liquid in theheat exchanger, while condensing the boiling gas and heats it aboveoutside air temperature and dissipates this heat to the outside air. Thefiller tube (27) allows liquid to come from the liquid to air exchangerand be inserted below where the gas bubbles are being released in theboiling gas separator (28) keeping the collector fluid loop (17) full ofliquid.

[0022] The system allows a small amount of boiling to take place, whichrejects heat to the atmosphere via the liquid to their heat exchanger.As long as boiling takes place the liquid in the side arm heat exchangerwill be heated by condensing the boiling gas. Only a small amount afluid will be forced into a fluid overflow steam condenser (4). Theadvantage of this system is that it has no moving parts and can easilydissipate all of the heat that the solar collector can gather from thesun.

1. A pressurized loop solar collectors system for delivering solarenergy from a roof mounted panel to a domestic hot water tank. a.Pressurization system capable of maintaining system pressures aboveatmospheric to increase the boiling point of the heat collection fluid.b. A means to prevent damage to solar collectors system from overheatingduring abnormal conditions c. The means to prevent damage from freezingin winter environments. d. A means to deliver heat to the hot water tankwith an easily adaptable internal heat exchanger. e. A better means todeliver heat to the hot water tank even with an external heat exchanger.2. A boiling activated collector over-temperature protection system,which utilizes no moving parts. a. The boiling gas separator, whichallows gas bubbles to heat a liquid to air heat exchanger. b. A fillertube, which allows the gas bubbles to heat the liquid to air heatexchanger, while keeping the system fluid loop full of liquid.
 3. Apressure activated collector over-temperature protection system whichutilizes solar collector air dampers as moving parts. a. A pressureactivated mechanical actuator, which opens before the systems regulatedpressure is reached. b. A set to of damper the valves, which controlairflow over the solar collector panel, so when opened the sun's energyis dissipated to the flowing air and when closed the sun's energy isdelivered to the fluid loop and hot water tank.
 4. A flexible umbilicalassembly, which carries and insulates the heat transfer fluid tubing,and includes all electrical connections between the solar collector andthe hot water tank.
 5. The system in claim 1, with a 220/115 VACcontroller and pump, with boiling activated over-temperature protectionof claim
 2. 6. The system in claim 1, with a 220/115 VAC controller andpump, with pressure activated over-temperature protection of claim
 3. 7.The system in claim 1, with a photovoltaic panel and low voltage (12VDC) pump, with boiling activated over-temperature protection of claim2.
 8. The system in claim 1, with a photovoltaic panel and low voltage(12 VDC) pump, with pressure activated over-temperature protection ofclaim 3.